JPH0975694A - Manufacture of hydrophilic membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a hydrophilic membrane which keeps a filtration velocity before modification and is free from the elution of a cellulose derivative during operation. SOLUTION: A hydrophobic membrane of an aromatic polymer is impregnated with the solution of a hydrophilic cellulose derivative at a temperature which is lower by 10 deg.C or more than the gel point or cloud point of the solution and washed with water of a temperature which is not lower by 20 deg.C or more than the gel point or cloud point of the solution.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a hydrophilic film by adsorbing a hydrophilic cellulose derivative on the hydrophobic film. The hydrophilic membrane obtained by the present invention is effectively used for microfiltration membranes, ultrafiltration membranes, medical membranes, etc., in which eluate from the membrane is extremely limited.

[0002]

2. Description of the Related Art A method for hydrophilizing a hydrophobic membrane has been known for a long time, in which a hydrophobic membrane is impregnated with a solution of a hydrophilic polymer and then a solvent is dried to attach the hydrophilic polymer. It can be said that hydrophilic polymers have been tried. It is also well known to use a cellulose derivative as the hydrophilic polymer. For example, Japanese Patent Publication Sho 5
6-16187 exemplifies methyl cellulose, ethyl cellulose, hydroxyethyl cellulose and hydroxypropyl cellulose.
In 08, hydroxypropyl cellulose having a molecular weight of 10,000 or more is used.

[0003]

The prior art focuses on making a hydrophobic film a hydrophilic film or insolubilizing a hydrophilic polymer, and it is not always necessary to prevent clogging by the hydrophilic polymer. In other words, it cannot be said that the method for maintaining the filtration rate before reforming without lowering has been sufficiently studied. The cellulose derivative used as the hydrophilic polymer is produced by chemically modifying powdery or flake-like cellulose. Therefore, among the cellulose derivatives, cellulose that is not completely dissolved in the solvent, remains in a dispersed state, and is not sufficiently chemically modified remains. When a hydrophobic membrane having a small pore size is impregnated with a solution containing such a cellulose derivative, a portion that is not completely dissolved blocks the pores of the membrane.

[0004] Many solutions of hydrophilic cellulose derivatives, for example, aqueous solutions, gel or become cloudy at a certain temperature or higher (for example, Nagura et al., Polymer Papers, Vol. 3).
8, No. 3, 133-127, 1981). Therefore, even if a solution of the cellulose derivative that has been separated by an appropriate method and completely dissolved is used, clogging still occurs when the hydrophobic membrane is impregnated in the gelled or clouded region. In the conventional method, the bubble point (for example, JIS
It cannot be said that the complete wettability that can be confirmed by K 3832) has been sufficiently examined. After the hydrophobic membrane is impregnated with a solution of a hydrophilic cellulose derivative, for example, an aqueous solution, the cellulose derivative other than that adsorbed on the surface of the hydrophobic membrane is removed by washing with water so that the cellulose derivative does not elute during actual use. However, if the temperature at this time is lower than the gelation or cloudiness region, the adsorbed cellulose derivative may be partially desorbed, and complete wettability may not be obtained.

The object of the present invention is to prevent the hydrophobic membrane from being clogged with the hydrophilic polymer, and to remove only the hydrophilic polymer which is not adsorbed on the surface of the hydrophobic membrane, so that the hydrophilic polymer before modification can be treated. It is an object of the present invention to provide a method for producing a hydrophilic membrane having complete wettability without reducing the filtration rate.

[0006]

MEANS FOR SOLVING THE PROBLEMS The present inventor first clogs a hydrophobic membrane by gelling or impregnating it with an aqueous solution of a cellulose derivative at a temperature 10 ° C. or more lower than the clouding temperature. It was found that the cellulose derivative not adsorbed on the membrane surface can be removed by finding out that there is no such substance, and then washing the impregnating solution with water whose temperature is not lower than the gelation or cloudiness temperature by 20 ° C. or more. They have found the present invention and completed the present invention.

That is, according to the present invention, a hydrophobic membrane of an aromatic polymer is impregnated with a solution of a hydrophilic cellulose derivative at a temperature lower by 10 ° C. or more than the gelation of the solution or the clouding temperature, and then the gelation of the solution. Or 20 than the clouding temperature
A method for producing a hydrophilic film, which comprises washing with water at a temperature not lower than 0 ° C.

The hydrophobic membrane used in the present invention comprises aromatic polymers such as aromatic polyethers, aromatic polyesters, aromatic polyamides, aromatic polyimides and aromatic polysulfones, each alone or as a mixture of two or more kinds. However, aromatic polysulfones such as polyether sulfone and polyallyl ether sulfone are particularly preferable because they have excellent basic properties such as chemical resistance, mechanical strength, and heat resistance. As the hydrophilic cellulose derivative used in the present invention, a relatively large hydrophilic substituent has a greater effect of imparting hydrophilicity, and for example, hydroxypropyl cellulose, hydroxypropylmethyl cellulose and the like are preferable, and these are used alone or in combination of two kinds. The above is used in combination.

In the above-mentioned JP-A-62-176508, the hydroxypropyl group is an effective hydrophobic bond residue for polysulfone, and in order to increase this number, hydroxypropyl cellulose having an average molecular weight of 10,000 or more must be used. However, according to the research by the present inventor, the content of methylcellulose and hydroxypropyl group is about 1/10 of that of hydroxypropylcellulose.
Hydroxypropylmethylcellulose or low-substituted hydroxypropylcellulose is more strongly adsorbed than hydroxypropylcellulose, and therefore the hydrophobic binding group for the aromatic residue is considered to be the glucose unit itself. Substituents impart hydrophilicity, but are believed to hinder hydrophobic bonds in reverse.

Therefore, in the present invention, the amount of these substituents is about 40% or less in order to exert a strong hydrophobic bond,
Further, it is preferable to use a cellulose derivative in the range of about 10% or more in order to impart hydrophilicity. The molecular weight of the hydrophilic cellulose derivative is not particularly limited, but a low molecular weight one having a number average molecular weight of about 2,000 to 8,000 can be made hydrophilic without blocking the pores even in a hydrophobic membrane having a relatively small pore size. It is possible to do so, which is preferable. On the other hand, if the molecular weight is less than 2,000, the binding force tends to decrease.

The above-mentioned cellulose derivative which is not completely dissolved can be removed by a usual molecular weight fractionation operation using a poor solvent. For example, since hydroxypropylmethylcellulose is partially dissolved in ethanol, if the supernatant liquid is collected, only a completely soluble component can be obtained. With respect to other cellulose derivatives, the components which are completely dissolved can be separated by the same method. By this operation, not only the completely dissolved component but also the low molecular weight component is separated at the same time. Therefore, it can be effectively applied to a film having a pore size of about 0.01 μm or more. The membrane may be hollow fiber or film.

Since hydrophilic cellulose derivatives are themselves surfactants, the hydrophobic membranes dried by these solutions will naturally wet. Therefore, usually, an aqueous solution can be used as the impregnating liquid, but in order to adjust the solubility,
Water-soluble organic solvents such as inorganic salts, inorganic alkalis, alcohols and acetone may be added alone or in combination of two or more. The hydrophobic membrane impregnated with the hydrophilic cellulose solution may be dried as described above, or may be undried. The concentration of the hydrophilic cellulose derivative in the impregnating solution is preferably about 50 to 2000 ppm. If it is less than 50 ppm, it may not be adsorbed on the entire surface of the film, and 2000
It does not make much sense because adsorption is not promoted even if it exceeds ppm. In the above-mentioned JP-A-62-176508, the hydrophobic membrane is contacted with the solution of the cellulose derivative for several hours or more. However, in the present invention, when the cellulose derivative having a large binding force as described above is used, the adsorption rate is high. The contact time of about 10 minutes or more and 2 hours or less is sufficient.

The method for impregnating the hydrophobic cellulose membrane with the hydrophilic cellulose derivative solution is not particularly limited, and any method such as immersing the membrane in the impregnating liquid, allowing the impregnating liquid to permeate through the membrane, or showering the impregnating liquid into the membrane can be used. It may be a method. As described above, when the temperature of the impregnating liquid is higher than the gelling or clouding temperature of the solution of the hydrophilic cellulose derivative, the aggregated cellulose derivative clogs the membrane, so the temperature must be at least below the gelling or clouding temperature. Although the gelation or clouding temperature of an aqueous cellulose derivative solution containing hydroxypropylcellulose and hydroxypropylmethylcellulose is shown in the above-mentioned document, even if these temperatures are not exceeded, as shown in Examples described later, in the vicinity of about 10 ° C or less. In addition, it is considered that a small amount of agglomerates have already been generated, and when the membrane is impregnated with such a solution, clogging occurs. Therefore, the temperature of the impregnating liquid is preferably 10 ° C. or more lower than the gelling or clouding temperature.

After impregnating the solution of the hydrophilic cellulose derivative described above, the cellulose derivative not adsorbed on the membrane is removed by washing with the same solvent as the solution, usually water. The solubility of the cellulose derivative adsorbed on the membrane is considered to be poorer than that of the already existing one, but the temperature at this time is 20 ° C higher than the gelation or clouding temperature of the impregnating liquid. It should not be lower than the above, and it is more preferable that the temperature is not lower than the gelling or clouding temperature. When washed with water at a temperature 20 ° C. or more lower than the gelation or clouding temperature, a part of the adsorbed cellulose derivative is desorbed from the membrane, and the complete wettability of the membrane is lost. The washing method is also not particularly limited, and any method such as immersing the membrane impregnated with the cellulose derivative solution in the washing solution at the above temperature, allowing the washing solution to permeate through the membrane, or showering the washing solution onto the membrane may be used. It is considered that the cellulose derivative binds to the membrane more strongly during this washing, and after washing for about 30 minutes, the cellulose derivative does not desorb even if it is brought into contact with water at a low temperature. The washed membrane is usually dried at a temperature below the glass transition temperature of the material of the membrane. The dried film has a hydrophilic property that naturally wets it when re-immersed in water.

The fact that the hydrophilic cellulose derivative is adsorbed on the entire hydrophobic membrane to form a hydrophilic membrane can be confirmed by measuring the bubble point as described above. For example, the bubble point of a membrane obtained by wetting the membrane before hydrophilic treatment with ethanol having a low surface tension and then replacing ethanol with water should be approximately the same as the baffle point of the membrane subjected to hydrophilic treatment wet with water. It can be judged that it is completely hydrophilic. Also, the fact that the hydrophilic membrane is not clogged means that the filtration rate of water (for example,
It can be confirmed by comparing the method of JIS K 3833) with the membrane before hydrophilic treatment. If these measured values are almost the same, it can be determined that there is no clogging.

[0016]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.

Example 1 (1) Fractionation of completely soluble hydroxypropylmethylcellulose Commercially available hydroxypropylmethylcellulose (hereinafter referred to as HPMC) having a number average molecular weight of about 11,000 and a methoxy group and a hydroxypropyl group of 29% and 9%, respectively. 10% by weight was dispersed in ethanol and left overnight. The transparent supernatant was separated and a completely soluble HPMC having an average molecular weight of 2500 was collected. The gelling or clouding temperature of these HPMC aqueous solutions is about 6 in the above literature.
0 ° C.

(2) Preparation of polysulfone hollow fiber type filter Not subjected to hydrophilic treatment, pore size is about 0.04 μm,
A so-called cartridge filter having an effective area of about 1.6 m ² shown in FIG. 1 is obtained by using a hollow fiber membrane having an outer diameter of 500 μm and 800 μm, and having a polyallyl ether sulfone (P-3500, Teijin Amoco Encinia Plastics Co., Ltd.) It was created. In the filter of FIG. 1, 1700 hollow fiber membranes 1 folded back in a loop are focused and fixed by a potting material at one end of a storage case 2 having a through hole 4 for the stock solution. The hollow fiber membrane is open at the tip of the focusing and fixing portion 3. This filter is attached to a housing (not shown) via an O-ring 6. The stock solution supplied from the inlet of the housing passes through the through hole 4 and is sent to the surface of the hollow fiber membrane 1. The liquid filtered from the surface of the hollow fiber membrane toward the inner surface flows out from the open end of the hollow fiber membrane at the tip of the focusing and fixing portion 3, and is taken out of the housing from the outlet 5 of the filtrate connected to the housing.

(3) Confirmation of the effect of removing the insoluble part The starting material HPMC and the separated 1000 ppm aqueous solution of HPMC were filtered at room temperature with the above filter. The filtration pressure of the raw material HPMC aqueous solution was more than doubled within 1 minute, but the filtration pressure of the separated HPMC aqueous solution hardly increased even after 1 hour.

(4) Effect of temperature of HPMC aqueous solution The 1000 ppm aqueous solution of HPMC thus separated was filtered through the above filter while changing the temperature. 18, 30, 35,
It was filtered at 40, 50 and 60 ° C. When the temperature was 40 ° C or lower, the filtration pressure hardly increased after 1 hour, but 50 ° C
With the above, the filtration pressure gradually increased, and after 1 hour, it reached more than double.

(5) Influence of temperature of washing water of HPMC aqueous solution 1000 pp of the separated HPMC was put on the above filter.
m water solution at 40 ℃ for 1 hour, then 18, 30, 4
Water at 0, 50, 60 and 90 ° C. was made to flow for 1 hour each to wash away HPMC not adsorbed on the membrane. It was then dried at 90 ° C. The filtration flow rate of water through these filters was measured. Water washed at 18 ° C. was not filtered even when the filtration pressure reached 200 KPa. In the case of washing at 30 ° C, water starts flowing after the filtration pressure rises to about 50 KPa, and the filtration pressure immediately decreases. After about 5 minutes, 8 L / 10.
The filtration rate was KPa · min. The product washed at a temperature of 40 ° C. or higher had a filtration rate of about 25 KPa and then water flowed out to give a stable filtration rate of 8 L / 10.
It became KPa · min. Therefore, it is considered that the HPMC once adsorbed was partially desorbed when washed at 30 ° C. or lower.

(6) Confirmation of Clogging by HPMC First, an aqueous ethanol solution was passed through a filter using a membrane not subjected to hydrophilic treatment, and then the filtration rate of water was measured. The filtration speed at this time is also 8 L / 10 KPa · min
Met. Therefore, as is clear from the above values, it can be judged that the hydrophilic membrane obtained by impregnating HPMC from which the insoluble portion has been removed at a predetermined temperature and washing is not clogged with the separated HPMC.

(7) Measurement of bubble point The above filter having a filtration rate of 8 L / 10 KPa · min was pressurized with 600 KPa of air, but no continuous bubbles were generated and any bubble point was 600 K.
It was larger than Pa and the hydrophilicity was judged to be perfect.

Example 2 A filter was prepared in the same manner as in Example 1 except that a polysulfone hollow fiber membrane having a pore size of 0.2 μm was used and used in the present invention.

(1) Confirmation of the effect of removing the insoluble portion This filter is used when the aqueous solution of the raw material HPMC is filtered.
The increase in filtration pressure was smaller than in the case of the 0.4 μm filter, but it increased to about 1.5 or more after 1 hour. On the other hand, when the separated aqueous solution of HPMC was filtered, the filtration pressure was not increased.

(2) Effect of temperature of HPMC aqueous solution The effect of the temperature of HPMC was examined in the same manner as in Example 1. The filtration pressure gradually increased at 50 ° C or higher, and reached about 50% or higher after 1 hour. No increase in filtration pressure was observed below 40 ° C.

(3) Influence of the temperature of the washing water of the HPMC aqueous solution The influence of the temperature of the washing water was investigated in the same manner as in Example 1.
The product washed at 18 ° C. did not flow water even when the filtration pressure reached 200 KPa. In the case of washing at 30 ° C, when the filtration pressure reaches about 20 KPa, water begins to flow and the filtration pressure decreases at the same time, and after 5 minutes, 15 L / 10 KPa · m.
in filtration rate. The product washed at 40 ° C. or higher immediately started to flow water, and the filtration rate was stable at 15 L / 10 KPa · min. Therefore, as in Example 1, it is considered that part of the adsorbed HPMC was desorbed when washed at 30 ° C. or lower.

(4) Confirmation of clogging by HPMC The filtration rate of the filter using the membrane not subjected to the hydrophilic treatment is also 15 L / 10 KPa.min.
As is clear from the above values, HP with the insoluble portion removed
It is considered that the hydrophilic film obtained by impregnation with MC at a predetermined temperature and washing was not clogged by the separated HPMC. On the other hand, an aqueous solution of raw material HPMC at 1
What was filtered after washing for 1 hour with water at 50 ° C. and then dried had a filtration rate of 11 L / 10 KPa · min. Therefore, without removing insoluble components, impregnation,
If the temperature is not the predetermined temperature for cleaning, it is determined that clogging has occurred and it was not removed even during cleaning.

(5) Measurement of bubble point The above filter having a filtration rate of 15 L / 10 KPa · min was heated with air of 600 KPa, but continuous bubbles were not generated and it was judged that the hydrophilicity was perfect. To be done.

Example 3 A similar experiment was carried out in Example 2 using commercially available hydroxypropyl cellulose (hereinafter referred to as HPC) having an average molecular weight of about 15,000 and a hydroxypropyl group of 62%. According to the above mentioned literature, the gelling or clouding temperature of this aqueous solution is about 50 ° C. Although the overall tendency was almost the same as that of HPMC, the temperature of the HPC aqueous solution was 40 ° C or lower and the temperature of the cleaning liquid was 50 ° C or higher in order to suppress clogging and make the hydrophilic property complete. there were.

[0031]

INDUSTRIAL APPLICABILITY As described above, the hydrophilic membrane obtained by the method of the present invention does not reduce the filtration rate before modification and has complete wettability. Furthermore, since the cellulose derivative that has not been adsorbed on the membrane has been removed, almost no cellulose derivative elutes during actual use, and thus the eluate from the membrane is extremely limited.
It is particularly useful for ultrafiltration membranes, medical membranes and the like.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a filter used in an example.

[Explanation of symbols]

 1 Hollow Fiber Membrane 2 Hollow Fiber Membrane Storage Case 3 Hollow Fiber Membrane Focusing and Fixing Portion 4 Water Passage Hole 5 Filtrate Outlet 6 O-ring

Claims (5)

[Claims] 1. An aromatic polymer-based hydrophobic membrane is impregnated with a solution of a hydrophilic cellulose derivative at a temperature 10 ° C. or more lower than the gelling or clouding temperature of the solution, and then the gelling or clouding temperature of the solution is exceeded. And a method for producing a hydrophilic film, which comprises washing with water at a temperature not lower than 20 ° C. 2. The method according to claim 1, wherein the aromatic polymer-based hydrophobic film is made of aromatic polysulfone. 3. The method according to claim 1 or 2, wherein the hydrophilic cellulose derivative is gelled or washed with water having a turbidity temperature or higher. 4. The solution of hydrophilic cellulose derivative is 50 to 50.
The manufacturing method according to claim 1, which is an aqueous solution having a concentration of 2000 ppm. 5. The method according to claim 1, wherein the hydrophilic cellulose derivative is hydroxypropylmethyl cellulose, hydroxypropyl cellulose or a mixture thereof.